The present invention was made with U.S. Government support, and the U.S. Government has certain rights in the invention.
The present invention relates to noise barrier apparatus for human ears and, more particularly, to in-ear noise barrier apparatus and over-the-ear noise barrier apparatus. The inventive apparatus may be used with or without integrated audio receivers. A particular aspect of the invention relates to an improved audio receiver which is fitted to a user's ear and which may be used in conjunction with an electronic stethoscope or other listening device such as a headset or similar device. The present invention may also be used with a typical, mechanical stethoscope or may be used as an ambient noise reducing ear plug.
Typical, mechanical stethoscopes comprise a stethoscope head and a pair of ear tubes that are coupled to the stethoscope head and biased together by a spring mechanism. Ear pieces or tips are mounted to the ends of the ear tubes for insertion into the user's ears. A column of air in the ear tubes transmits sounds detected by the stethoscope head to the ear pieces. The spring mechanism helps hold the ear pieces positioned in the user's ears. An electronic stethoscope may also have a speaker (i.e. earphone) or other electronic device in or next to the ear piece to assist in listening.
How the earpiece fits in the user's ear can affect both the comfort of the user and the overall effectiveness of the earpiece, i.e., the ability of the user to hear the sounds broadcast by the earpiece. FIG. 1 illustrates various parts of a human ear 10 and particularly shows the complex shape of the outer ear. The external or outer ear includes: the helix 12, a curved fold forming most of the rim of the external ear; the antihelix ridge 14, the inward curving ridge of the auricle (projecting outer portion) of the external ear; the triangular fossa or depression 16 between the antihelix 14 and the helix 12; the concha region 18, the larger depression near the opening into the ear canal; the ear lobe 20, the soft, pendulous, lower part of the external ear; the tragus 22, the fleshy prominence at the front of the external opening of the ear; the antitragus 24, the fleshy prominence opposite the tragus 22; the iscisua or notch 26 between the tragus 22 and antitragus 24; and the rim of or entrance 28 to the ear canal 30. The ear canal 30 provides a passageway between the external ear and the tympanic membrane or ear drum 32. Part of the jaw line interface 34 is shown extending downward from the ear 10.
It is generally desirable for the ear pieces to be biased or pressed against the user's ear so that a substantially airtight seal is formed. A good seal may prevent a significant amount of the ambient sounds or noise from reaching the user's ear drum via the ear canal through the entrance 28 to the ear canal and interfering with the stethoscope sounds. Achieving such an airtight seal, however, can be difficult and cause considerable discomfort to the user due to the relative hardness and shape of the ear pieces.
Typical earpieces for stethoscopes have a generally ball-like configuration that does not conform well to the complex shape of the human ear. In addition, the earpieces are often made from a relatively hard plastic material. When the earpiece is placed in the user's ear, it contacts and applies a force against a small area around the rim of or entrance 28 to the ear canal 30. The entrance 28 to the ear canal 30, however, can be particularly sensitive to pressure. The combination of a small contact area and the spring force from the spring mechanism of the ear tubes, therefore, oftentimes causes pain and discomfort to the user after a relatively short period of time. Furthermore, due to their bulbous configuration, the typical earpieces do not generally form a good seal with the ear and, therefore, do not serve well to reduce the amount of noise entering the user's ear canal 30 through the entrance 28.
The problems discussed above in connection with in-ear noise-barrier apparatus also apply to over-the-ear noise barrier apparatus.
In addition to not providing a very effective noise seal, prior art noise barrier apparatus also do very little to dampen and may even increase noise due to vibration of the noise barrier apparatus that may be transmitted through the earpiece structure to the user's ear. When an earpiece is subjected to an oscillating force, e.g. an external acoustic pressure wave (such as noise), the earpiece structure will react or respond to the oscillating force in a predictable vibrating manner which results in noise being generated on the internal side of the earpiece (as opposed to leaking past the earpiece) to the user's eardrum.
The oscillating response of an earpiece to an oscillating force is similar to the operation of an electromagnetic voice-coil in a conventional loud speaker. The voice-coil oscillates in response to an electrical signal at the coil and causes the speaker cone to vibrate and generate an acoustic pressure wave that results in sound. Similarly, an earpiece will oscillate or vibrate in response to a time varying force such as noise resulting in the generation of an acoustic pressure wave at the tip of the earpiece. This oscillation or vibration of the earpiece is analogous to the undamped or insufficiently damped oscillation of a linear spring-mass system. The acoustic pressure wave is then transmitted along the user's ear canal to the eardrum. As a result, unwanted noise is thereby transmitted to the user's ear.
Prior art cushions provided on both in-ear and over-the-ear noise barrier apparatus, are typically formed of materials, such as foamed polyurethane, that are elastically deformable such that, although they deform when a force is applied thereto, they quickly rebound to their original shape once the force is removed. While these cushions are soft, compliant, and are considered by most users to be reasonably comfortable, they perform other functions poorly. Most importantly, such elastically deformable materials act like linear springs such that, once acted upon by external acoustic waves, they will oscillate so as to essentially conduct or propagate the external wave through the cushion material. This oscillation of the cushion material causes acoustic waves to be generated within the audio chamber of the noise barrier device (including the ear canal itself), thus generating considerable noise and pressure incident in the ear canal.